It is known to produce brominated styrenic polymers by brominating a styrenic polymer in a suitable solvent using bromine chloride and an antimony trihalide catalyst. See in this connection U.S. Pat. No. 4,352,909 to Barda et al., and U.S. Pat. No. 5,723,549 to Dever et al., the full disclosures of which are incorporated herein by reference. One of the products made in this way is a commercial product available under the trademark Pyro-Chek 68PB.
In order to minimize contamination of the brominated styrenic polymer product by antimony catalyst residues, it has been the practice to subject the bromination reaction mass to an aqueous work up and to precipitate the antimony catalyst residues from the aqueous phase first as the oxychloride and then as the sulfide. In order to operate the process on a more efficient cost-effectiveness basis, it is desired to recover as much of the antimony catalyst residues as possible and to recycle them use as catalyst in the bromination step. It would be especially advantageous if the recovered product could be reused as catalyst in the process without adversely affecting either the bromination reaction or the properties of the brominated flame retardant product formed therewith.
However, antimony catalyst recovery processes and halogenation processes employing the same have several drawbacks, including, but not limited to, the formation of solids that are insoluble in the solvents and/or acids used in the halogenation processes. These solids, typically higher oxides of antimony such as antimony (IV) and (V) oxides cause many processing problems such as, for example, clogging processing equipment, etc. and also cause the loss of a portion of the costly antimony. For example, U.S. Pat. No. 6,994,148, which is incorporated herein by reference, discloses an antimony trihalide catalyst recovery process whereby antimony halide catalyst residues are recovered from a styrene polymer bromination process. This recovery is facilitated by mixing the reaction mass formed in the bromination process with hydrochloric acid, hydrobromic acid, or both, at least once such that the antimony halide catalyst residues are thereby recovered in an acidic aqueous phase. However, the inventors hereof have discovered that this process also has some of the drawbacks discussed above.
Thus, there exists a need in the art for antimony catalyst recovery processes that overcomes these and other drawbacks of existing recovery processes.